This invention concerns a lockable hitch pin assembly which is ideally suited for use on a three-point hitch as found on farm tractors and other agricultural equipment. Generally, a three-point hitch includes three actuating links connected to a hydraulic lift cylinder operated by the hydraulic system of a tractor. The links are adapted to receive a transverse mounted crossbar or other hitching equipment, such as a pin and yoke. The crossbar generally extends through the ends of the bottom two links. The bar is retained in position by hitch pins positioned in transverse holes provided in each end of the crossbar. Various harvesting devices and other farm machinery may be secured to or towed by the tractor through the bar.
Generally, the standard hitch pin in use today consists of a pin having a head and pull ring pivotally attached to the head. The pull ring is provided as a means for extracting the hitch pin from the operative or installed position. This standard hitch pin can provide unsatisfactory results. More specifically, the pin can be accidently removed by contact with foreign material, such as underbrush, or severe shocks as are frequently found in farming equipment operations.
U.S. Pat. No. 2,856,806 to Gibbons discloses a coupling or hitch pin with a spring loaded retractable bolt retained within the pin. To position the pin in place to retain the crossbar, the bolt is first retracted within the pin. The pivoting pull ring is moved downwardly to a position inboard of the retractable bolt. The bolt is then allowed to return to its normal extended position whereupon the pull ring is held adjacent to the bolt shaft. Such a design, while an improvement over the standard hitch pin, is not without its disadvantages. Specifically, the pull ring is left to swing free behind the bolt and is susceptible to being snagged and elongated. Once deformed in this manner, the ring can be pivoted and moved over the bolt, and thus the pin accidently dislodged. Additionally, the bolt must extend a substantial distance out of the pin with this design, and is thus generally more susceptible to damage, as well as being accidentally directly retracted by contact with foreign material, allowing the pin to dislodge.
U.S. Pat. No. 3,926,089 Ruebig et al. discloses a hitch pin having a looped pull ring rotatably attached to the top of the pin. A notch is provided in the lower end of the pin and is adapted for receiving the pull ring. In use, the pin is inserted into its mating hole. The pull ring is then rotated downwardly and inserted into the notch in the pin. The pull ring is fabricated of a spring steel material and must be deformed slightly to be inserted in the notch. The spring force created by this deformation serves to retain the pull ring within its notch. However, with regular use, the pull ring tends to take on a permanent deformation. This deformation and its associated loss of spring tension serves to greatly reduce the effectiveness of the locking mechanism. Additionally, the heavy duty nature of the equipment used in farming applications would require a pull ring of such strength as to make installation and removal of this device by hand very difficult. Furthermore, locking pins of this type are also prone to be released by contact and snagging with foreign material.
A need exists, therefore, for a hitch pin which can be securely locked into place which is substantially immune to accidental release. Such a locking hitch pin would be reliable and simple to install yet capable of withstanding rigorous, heavy duty usage.